Etch rate detection for anti-reflective coating layer and absorber layer etching

ABSTRACT

A method and apparatus for etching a photomask substrate with enhanced process monitoring is provided. In one embodiment, a method of determining an etching endpoint includes performing an etching process on a first tantalum containing layer through a patterned mask layer, directing a radiation source having a first wavelength from about 200 nm and about 800 nm to an area uncovered by the patterned mask layer, collecting an optical signal reflected from the area covered by the patterned mask layer, analyzing a waveform obtained the reflected optical signal reflected from the substrate from a first time point to a second time point, and determining a first endpoint of the etching process when a slope of the waveform is changed about 5 percent from the first time point to the second time point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/543,222, filed Jul. 6, 2012, now issued U.S Pat. No. 8,900,469, whichclaims benefit of U.S. Provisional Application Ser. No. 61/577,318 filedDec. 19, 2011, both of which are incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to the fabricationof integrated circuits and to the fabrication of photomasks useful inthe manufacture of integrated circuits.

2. Description of the Related Art

In the manufacture of integrated circuits (IC), or chips, patternsrepresenting different layers of the chip are created by a chipdesigner. A series of reusable masks, or photomasks, are created fromthese patterns in order to transfer the design of each chip layer onto asemiconductor substrate during the manufacturing process. Mask patterngeneration systems use precision lasers or electron beams to image thedesign of each layer of the chip onto a respective mask. The masks arethen used much like photographic negatives to transfer the circuitpatterns for each layer onto a semiconductor substrate. These layers arebuilt up using a sequence of processes and translate into the tinytransistors and electrical circuits that comprise each completed chip.Thus, any defects in the mask may be transferred to the chip,potentially adversely affecting performance. Defects that are severeenough may render the mask completely useless. Typically, a set of 15 to30 masks is used to construct a chip and can be used repeatedly.

The next generation photomask as further discussed below is formed on alow thermal expansion glass or a quartz substrate having a multilayerfilm stack disposed thereon. The multilayer film stack may include ananti-reflective coating layer, an absorber layer, a capping layer, and areflective multi-material layer. When manufacturing the photomask, aphotoresist layer is disposed on the film stack to facilitatetransferring features into the film stack during the subsequentpatterning processes. During the patterning process, the circuit designis written onto the photomask by exposing portions of the photoresist toextreme ultraviolet light or ultraviolet light, making the exposedportions soluble in a developing solution. The soluble portion of theresist is then removed, allowing the underlying film stack exposedthrough the remaining photoresist be etched. The etch process removesthe film stack from the photomask at locations where the resist wasremoved, i.e., the exposed film stack is removed.

With the shrink of critical dimensions (CD), present optical lithographyis approaching a technological limit at the 45 nanometer (nm) technologynode. Next generation lithography (NGL) is expected to replace theconventional optical lithography method, for example, in the 32 nmtechnology node and beyond. There are several NGL candidates, such asextreme ultraviolet (EUV) lithography (EUVL), electron projectionlithography (EPL), ion projection lithography (IPL), nano-imprint, andX-ray lithography. Among these, EUVL is the most likely successor due tothe fact that EUVL has most of the properties of optical lithography,which is a more mature technology as compared with other NGL methods.

Accordingly, the film stack is being developed to have a new film schemeso as to work with the EUV technology to facilitate forming thephotomask with desired features disposed thereon. The film stack mayinclude multiple layers with different new materials to be etched toform the desired features. Imprecise etch process and etch endpointcontrol may result in critical dimension (CD) bias, poor criticaldimension (CD) uniformity, undesired cross sectional profile and etchcritical dimension (CD) linearity and unwanted defects. It is believedthat EUV technology may provide good CD uniformity, less etching bias,desired linearity, less line edge roughness, and high thicknessuniformity and less defectivity.

As the new developed film stack described above includes ananti-reflective coating layer, an absorber layer, a capping and areflective multi-material layer, obtaining precise etching endpoint foreach of the layers being etched is becoming more and more difficult.Inaccurate etch endpoint control will often result in etch bias whichmay result in accurate transfer of the patterns to the film stack withdesired critical dimension less than about 5 μm, such as about 50 nm toabout 500 nm. This results in non-uniformity of the etched features ofthe photomask and correspondingly diminishes the ability to producefeatures for devices having small critical dimensions using thephotomask. As the critical dimensions of photomask continue to shrink,the importance of accurate etching endpoint control increases. Thus, anaccurate etching process endpoint control to the film stack disposed onthe photomask for EUV technology is highly desirable.

Therefore, there is an ongoing need for improved etching endpointprocess control in photomask fabrication, including improved apparatusand methods for collecting etch rate data and determining processendpoints.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for etching aphotomask substrate with enhanced process monitoring, for example, byproviding for optical monitoring at certain regions of the photomask toobtain desired etch rate or thickness loss. In one embodiment, a methodof determining an etching endpoint of a tantalum containing layerdisposed on a substrate during an etching process includes performing anetching process on a first tantalum containing layer disposed on a firstsurface of a substrate through a patterned mask layer in a plasma etchchamber, directing radiation having a first wavelength from about 200 nmand about 800 nm to an area of the first tantalum containing layeruncovered by the patterned mask layer during the etching process,collecting an optical signal reflected from the area uncovered by thepatterned mask layer, analyzing a waveform obtained from the reflectedoptical signal, and determining a first endpoint of the etching processwhen a slope of the waveform change by about 5 percent or greater.

In another embodiment, a method of determining an etching endpoint of atantalum containing layer disposed on a substrate during an etchingprocess includes performing an etching process on a tantalum and oxygencontaining layer disposed on a first surface of a substrate through apatterned mask layer in a plasma etch chamber, directing a firstradiation source having a first wavelength from about 200 nm and about800 nm from the first surface of the substrate to an area uncovered bythe patterned mask layer, collecting a first optical signal reflectedfrom the area covered by the patterned mask layer to obtain a firstwaveform from the reflected first optical signal, analyzing a firstwaveform obtained the reflected first optical signal reflected from thefirst surface of the substrate from a first time point to a second timepoint, determining a first endpoint of the etching process when a slopeof the waveform is changed about 5 percent or greater from the firsttime point to the second time point, continuing etching a tantalumcontaining and oxygen free layer disposed between the tantalumcontaining and oxygen free layer and substrate, directing a secondradiation source having a second wavelength from about 200 nm and about800 nm from the first surface of the substrate to an area uncovered bythe patterned mask layer and the etched tantalum containing and oxygenfree layer, collecting a second optical signal reflected from the areacovered by the patterned mask layer and the etched tantalum and oxygencontaining layer to obtain a second waveform from the reflected secondoptical signal, analyzing a second waveform obtained the reflectedsecond optical signal reflected from the first surface of the substratefrom a third time point to a fourth time point, and determining a secondendpoint of the etching process when a slope of the waveform is changedabout 5 percent or greater from the third time point to the fourth timepoint.

In yet another embodiment, a method of determining an etching endpointof a tantalum containing layer disposed on a substrate during an etchingprocess includes performing an etching process on a tantalum and oxygencontaining layer disposed on a first surface of a substrate through apatterned mask layer in a plasma etch chamber, directing a firstradiation source having a first wavelength from about 220 nm from thefirst surface of the substrate to an area uncovered by the patternedmask layer, collecting a first optical signal reflected from the areacovered by the patterned mask layer to obtain a first waveform from thereflected first optical signal, analyzing a first waveform obtained thereflected first optical signal reflected from the first surface of thesubstrate, determining a first endpoint of the etching process when thereflected first optical signal becomes saturated, continuing etching atantalum containing and oxygen free layer disposed between the tantalumcontaining and oxygen free layer and substrate, directing a secondradiation source having a second wavelength about 230 nm from the firstsurface of the substrate to an area uncovered by the patterned masklayer and the etched tantalum containing and oxygen free layer,collecting a second optical signal reflected from the area covered bythe patterned mask layer and the etched tantalum and oxygen containinglayer to obtain a second waveform from the reflected second opticalsignal, analyzing a second waveform obtained the reflected secondoptical signal reflected from the first surface of the substrate, anddetermining a second endpoint of the etching process when the reflectedsecond optical signal becomes saturated.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the invention are attained and can be understood in detail, amore particular description of the invention, briefly summarized above,may be had by reference to the embodiments thereof which are illustratedin the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates a etch chamber incorporating one embodiment of thepresent invention;

FIG. 2 illustrates schematically structures of one embodiment of thephotomasks during fabrication;

FIG. 3 illustrates a flow diagram regarding an endpoint determinationprocess during fabrication process depicted in FIG. 2;

FIG. 4A illustrates one embodiment of optical signals detected for etchrate determination for etching an antireflective coating layer; and

FIG. 4B illustrates one embodiment of optical signals detected for etchrate determination for etching an bulk absorber layer.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

The present invention provides a method and apparatus for etching aphotomask substrate with enhanced process monitoring, for example, byproviding for optical monitoring at certain regions of the photomask toobtain desired etch rate or endpoint determination. Although thediscussions and illustrative examples focus on the etching ratedetection and process endpoint determination during an etching processof an anti-reflective coating layer and an absorber layer disposed on aphotomask substrate, various embodiments of the invention can also beadapted for process monitoring of other suitable substrates, includingtransparent or dielectric substrates, or optical disks.

FIG. 1 is a schematic cross sectional view of a plasma etch chamber 10in accordance with one embodiment of the invention. Suitable plasma etchchambers that may be adapted to practice the invention include theTetra™ II photomask etch chamber or the Decoupled Plasma Source (DPS™)chamber available from Applied Materials, Inc., of Santa Clara, Calif.Other suitably adapted process chambers may also be used in connectionwith embodiments of the invention, including, for example, capacitivecoupled parallel plate chambers and magnetically enhanced ion etchchambers, as well as inductively coupled plasma etch chambers ofdifferent designs. The particular embodiment of the etch chamber 10shown herein is provided for illustrative purposes and should not beused to limit the scope of the invention. It is contemplated that theinvention may be utilized in other processing systems, including thosefrom other manufacturers.

The etch chamber 10 generally includes a cylindrical sidewall or chamberbody 12, an energy transparent chamber lid 13 mounted on the body 12,and a chamber bottom 17. The chamber lid 13 may be flat, rectangular,arcuate, conical, dome or multi-radius shaped. At least one inductivecoil 26 is disposed above at least a portion of the chamber lid 13. Inthe embodiment depicted in FIG. 1, two concentric coils 26 are shown.The chamber body 12 and the chamber bottom 17 of the etch chamber 10 canbe made of a metal, such as anodized aluminum, and the chamber lid 13can be made of an energy transparent material such as a ceramic or otherdielectric material.

A substrate support member 16 is disposed in the etch chamber 10 tosupport a substrate 102 during processing. The support member 16 may bea conventional mechanical or electrostatic chuck with at least a portionof the support member 16 being electrically conductive and capable ofserving as a process bias cathode. While not shown, a photomask adaptermay be used to secure the photomask on the support member 16. Thephotomask adapter generally includes a lower portion configured to coveran upper portion of the support member and a top portion having anopening that is sized and shaped to hold a photomask. In one embodiment,the top portion of the photomask adapter has a square opening. Asuitable photomask adapter is disclosed in U.S. Pat. No. 6,251,217,issued on Jun. 26, 2001, which is incorporated herein by reference.

Process gases are introduced into the etch chamber 10 from a process gassource 48 through a gas distributor 22 peripherally disposed about thesupport member 16 and/or disposed in the chamber lid 13. Mass flowcontrollers (not shown) for each process gas, or alternatively, formixtures of the process gas, are disposed between the etch chamber 10and the process gas source 48 to regulate the respective flow rates ofthe process gases.

A plasma zone 14 is defined in the etch chamber 10 between the substratesupport member 16 and the chamber lid 13. A plasma is generated in theplasma zone 14 from the process gases by supplying power from a powersupply 27 to the inductive coils 26 through an RF match network 35. Thesupport member 16 may include an electrode disposed therein, which ispowered by an electrode power supply 28 and generates a capacitiveelectric field in the etch chamber 10 through an RF match network 25.Typically, RF power is applied to the electrode in the support member 16while the body 12 is electrically grounded. The capacitive electricfield, which is transverse to the plane of the support member 16,influences the directionality of charged species to provide moreanisotropic etching of the substrate 102.

Process gases and etchant byproducts are exhausted from the etch chamber10 through an exhaust port 34 to an exhaust system 30. The exhaust port34 may be disposed in the bottom 17 of the etch chamber 10 or may bedisposed in the body 12 of the etch chamber 10 for removal of processgases. A throttle valve 32 is provided in the exhaust port 34 forcontrolling the pressure in the etch chamber 10.

In one embodiment, an etch rate (i.e., endpoint) detection system 164operatively coupled to the etch chamber 10. At least one optical accessports or viewports, are provided in different regions of the substratesupport member 16, lid 13 and/or chamber body 12. In the example shownin FIG. 1, the optical access port comprises respectively a window 192at a central region 16C of the chamber lid 13. The endpoint detectionsystem 164 is configured to detect optical signals through the window192. It is noted that more than one window may be formed in the chamberlid 13 or other locations of the etch chamber 10 which allows opticalmonitoring of various locations on a photomask substrate 102 from itssurface during etching. Alternatively, different numbers of windows maybe provided at other locations of the lid 13, chamber body 12 and/orsubstrate support member 16 as needed. For example, a side window 193may be formed on the chamber wall 15 having a second etch rate detectionsystem 195 coupled thereto to facilitate etch rate determinationprocess. A camera 199 may be disposed adjacent to the etch ratedetection system 164 to assist viewing the substrate 102 through thesame optical view port as the endpoint detection system 164 so as toconfirm that the radiation from the etch rate detection system 164 isdirected to a correct location on the substrate surface for detection.

In general, a larger window facilitates the installation of opticalcomponents. However, the size of the window, especially in the centralregion 16C of the chamber lid 13, is selected to be sufficiently largefor optical monitoring, yet small enough to avoid potential adverseimpact for the RF interference. Selecting a small window also improvesthe lateral temperature uniformity of the chamber lid 13. The opticalaccess port may generally comprise a flat window made of quartz or othermaterials that transmit light over a broad wavelength spectrum andresist plasma etching. A more detailed discussion of different opticalconfigurations will be provided further below.

The endpoint detection system 164 comprises optical setup for operatingin at least one of reflection, interferometry or transmission modes, andis configured for different types of measurements such as reflectance ortransmittance, interferometry, or optical emission spectroscopy.Depending on the application of interest, e.g., the material layers orsubstrate structure being processed, endpoints may be detected based ona change in the reflectance or transmittance intensities, the number ofinterference fringes, or changes in optical emission intensities atspecific wavelengths, or a combination thereof. In one particularembodiment depicted therein, the endpoint detection system 164 isconfigured to detect a process endpoint based on a change in thereflectance reflected from an etched substrate surface.

The reflection mode of operation allows reflectance (or reflectometry)and interferometric measurement to be performed. The endpoint detectionsystem 164 generally comprises a light source 166, a focusing assembly168 for focusing an incident optical beam 176 from the light source 166onto a discreet area (spot) 180 on the surface of substrate 102, and aphotodetector 170 for measuring the intensity of a reflected opticalbeam 178 reflected off the spot 180 of the substrate 102. Any adjustmentmechanism 196 may be provided to set an angle of incidence 197 of thebeam 176 so that the spot 180 may be selectively located on a desiredlocation on the substrate 102. The adjustment mechanism 196 may be anactuator, set screw or other device suitable for setting the angle ofincidence 197 by moving (tilting) the endpoint detection system 164itself or a component therein, such as with an optical beam positioned184, further discussed below. The photodetector 170 may be a singlewavelength or multi-wavelength detector, or a spectrometer. Based on themeasured signal of the reflected optical beam 178, a computer system 172calculates portions of the real-time waveform and compares it with astored characteristic waveform pattern to extract information relatingto the etch process. In one embodiment, the calculation may be based onslope changes or other characteristic changes in the detected signals,either in reflection or transmission mode, for example, when a film isetched to a target depth. Alternatively, the calculation may be based oninterferometric signals as the depth of a trench or the thickness of afilm changes during etching. In other embodiments, more detailedcalculations may be performed based on interferometric signals obtainedover a wide spectrum in order to determine the depth or thickness at anypoint in the etch process to determine etch rate of the object beingetched.

The light source 166 may be monochromatic, polychromatic, white light,or other suitable light source. In general, the optical signal from thereflected optical beam 178 may be analyzed to extract informationregarding the presence or absence of a layer (e.g., an anti-reflectivecoating layer or an absorber layer), or the thickness of certainmaterial layers within the spot 180. The intensity of the incidentoptical beam 176 is selected to be sufficiently high to provide areflected optical beam 178 with a measurable intensity. The lamp canalso be switched on and off to subtract background light. In oneembodiment, the light source 166 provides polychromatic light, e.g.,from an Hg—Cd lamp, an arc lamp, or a light emitting diode (LED) or LEDarray, which generate light in wavelength ranges from about 170 nm toabout 800 nm, or about 200 to 800 nm, for example about 250 nm to about800 nm respectively. The polychromatic light source 166 can be filteredto provide an incident optical beam 176 having selected frequencies.Color filters can be placed in front of the photodetector 170 to filterout all wavelengths except for the desired wavelength of light, prior tomeasuring the intensity of the reflected optical beam 178 entering thephotodetector 170. The light can be analyzed by a spectrometer (arraydetector with a wavelength-dispersive element) to provide data over awide wavelength range, such as ultraviolet to visible, from about 200 nmto 800 nm. The light source 166 can also comprise a flash lamp, e.g., aXe or other halogen lamp, or a monochromatic light source that providesoptical emission at a selected wavelength, for example, a He—Ne orND-YAG laser. The light source may be configured to operate in acontinuous or pulsed mode. Alternatively, the wavelength range may beexpanded into the deep UV as low as 170 nm or beyond using opticalmaterials with stable deep UV transmission and purging air paths withinert gas or other suitable carrier gas, such as nitrogen gas.

One or more convex focusing lenses 174A, 174B may be used to focus theincident optical beam 176 to the spot 180 on the substrate surface, andto focus the reflected optical beam 178 back on the active surface ofphotodetector 170. The spot 180 should be sufficiently large tocompensate for variations in surface topography of the substrate 102 anddevice design features. This enables detection of etch endpoints forhigh aspect ratio features having small openings, such as vias or deepnarrow trenches, which may be densely present or more isolated. The areaof the reflected optical beam 178 should be sufficiently large toactivate a large portion of the active light-detecting surface of thephotodetector 170. The incident and reflected optical beams 176, 178 aredirected through the transparent window 192 in the etch chamber 10 thatallows the optical beams to pass in and out of the processingenvironment.

The diameter of the beam spot 180 is generally about 2 mm to about 10mm. However, if the beam spot 180 encompasses large isolated areas ofthe substrate 102 containing only a small number of etched features, itmay be necessary to use a larger beam spot in order to encompass agreater number of etched features. The size of the beam spot cantherefore be optimized, depending on the design features for aparticular device. If the signal is sufficient, a large beam spot orfield of view will enable process control without precisely matching theposition of the substrate support hole and the etched area of thesubstrate giving rise to the signal.

Optionally, the optical beam positioner 184 may be used to move theincident optical beam 176 across the substrate 102 to locate a suitableportion of the substrate surface on which to position the beam spot 180to monitor an etching process. The optical beam positioner 184 mayinclude one or more primary mirrors 186 that rotate at small angles todeflect the optical beam from the light source 166 onto differentpositions of the substrate surface. Additional secondary mirrors may beused (not shown) to direct the reflected optical beam 178 on thephotodetector 170. The optical beam positioner 184 may also be used toscan the optical beam in a raster pattern across the surface of thesubstrate 102. In this embodiment, the optical beam positioner 184comprises a scanning assembly consisting of a movable stage (not shown),upon which the light source 166, the focusing assembly 168 and thephotodetector 170 are mounted. The movable stage can be moved throughset intervals by a drive mechanism, such as a stepper motor orgalvanometer, to scan the beam spot 180 across the substrate 102.

The photodetector 170 comprises a light-sensitive electronic component,such as a photovoltaic cell, photodiode, phototransistor, orphotomultiplier, which provides a signal in response to a measuredintensity of the reflected optical beam 178. The signal can be in theform of a change in the level of a current passing through an electricalcomponent or a change in a voltage applied across an electricalcomponent. The photodetector 170 can also comprise a spectrometer (arraydetector with a wavelength-dispersive element) to provide data over awide wavelength range, such as ultraviolet to visible, from about 170 nmto 800 nm. The reflected optical beam 178 undergoes constructive and/ordestructive interference which increases or decreases the intensity ofthe optical beam, and the photodetector 170 provides an electricaloutput signal in relation to the measured intensity of the reflectedoptical beam 178. The electrical output signal is plotted as a functionof time to provide a spectrum having numerous waveform patternscorresponding to the varying intensity of the reflected optical beam178.

In another embodiment, a plasma signal, e.g., plasma emission generatedin the plasma zone, may also be collected for detection as needed fordifferent process requirements.

A computer program on a computer system 172 analyzes the shape of themeasured waveform pattern of the reflected optical beam 178 to determinethe endpoint of the etching process. The waveform generally has asinusoidal-like oscillating shape, with the trough of each wavelengthoccurring when the depth of the etched feature causes the return signalto be 180 degrees out of phase with the return signal reflected by theoverlaying layer. The endpoint may be determined by calculating the etchrate using the measured waveform, phase information of the measuredwaveform and/or comparison of the measured waveform to a referencewaveform. As such, the period of the interference signal may be used tocalculate the depth and etch rate. The program may also operate on themeasured waveform to detect a characteristic waveform, such as, aninflection point indicative of a phase difference between lightreflected from different layers. The operations can be simple mathematicoperations, such as evaluating a moving derivative to detect aninflection point.

FIG. 2 shows a photomask substrate 102 with a film stack 200 disposedthereon for etching that may be monitored by different etch ratedetection techniques of the present invention. The film stack 200disposed on the photomask substrate 102 that may be utilized to formdesired features (i.e., openings 218) in the film stack 200. As theexemplary embodiment depicted in FIG. 2, the photomask substrate 102 maybe a quartz substrate or a special low thermal expansion glasssubstrate. The photomask substrate 102 has a rectangular shape havingsides between about 5 inches to about 9 inches in length. The photomasksubstrate 102 may be between about 0.15 inches and about 0.25 inchesthick. In one embodiment, the photomask substrate 102 is about 0.25inches thick. An optional chromium containing layer 204, such as achromium nitride (CrN) layer may be disposed to a backside of thephotomask substrate 102 as needed.

An EUV reflective multi-material layer 206 is disposed on the photomasksubstrate 102. The reflective multi-material layer 206 may include atleast one molybdenum layer 206 a and a silicon layer 206 b. Although theembodiment depicted in FIG. 2 shows five pairs of molybdenum layer 206 aand silicon layer 206 b (alternating molybdenum layers 206 a and thesilicon layers 206 b repeatedly formed on the photomask substrate 102),it is noted that number of molybdenum layers 206 a and the siliconlayers 206 b may be varied based on different process needs. In oneparticular embodiment, forty pairs of molybdenum layers 206 a and thesilicon layers 206 b may be deposited to form the reflectivemulti-material layer 206. In one embodiment, the thickness of eachsingle molybdenum layer 206 a may be controlled at between about 10 Åand about 100 Å, such as about 30 Å, and the thickness of the eachsingle silicon layer 106 b may be controlled at between about 10 Å andabout 100 Å, such as about 40 Å. The reflective multi-material layer 206may have a total thickness between about 100 Å and about 5000 Å. Thereflective multi-material layer 206 may have an EUV light reflectivityof up to 70% at 13.5 nm wavelength. The reflective multi-material layer206 may have a total thickness between about 70 nm and about 140 nm.

Subsequently, a capping layer 208 is disposed on the reflectivemulti-material layer 206. The capping layer 208 may be fabricated by ametallic material, such as ruthenium (Ru) material, zirconium (Zr)material, or any other suitable material. In the embodiment depicted inFIG. 2, the capping layer 208 is a ruthenium (Ru) layer. The cappinglayer 208 has a thickness between about 1 nm and about 10 nm.

An absorber layer 216 may then be disposed on the capping layer 208. Theabsorber layer 216 is an opaque and light-shielding layer configured toabsorb portion of the light generated during the lithography process.The absorber layer 216 may be in form of a single layer or a multi-layerstructure, such as including an antireflective coating layer 212disposed on a bulk absorber layer 210, as the embodiments depicted inFIG. 2. In one embodiment, the absorber layer 216 has a total filmthickness between about 50 nm and about 200 nm. The total thickness ofthe absorber layer 216 advantageously facilitates meeting the strictoverall etch profile tolerance for EUV masks in sub-45 nm technologynode applications.

In one embodiment, the bulk absorber layer 210 may comprisetantalum-based materials with essentially no oxygen, for exampletantalum silicide based materials, such as TaSi, nitrogenized tantalumboride-based materials, such as TaBN, and tantalum nitride-basedmaterials, such as TaN. The antireflective coating layer 212 may befabricated from a tantalum and oxygen-based materials. The compositionof the antireflective coating layer 212 corresponds to the compositionof the bulk absorber layer 210 and may comprise oxidized andnitrogenized tantalum and silicon based materials, such as TaSiON, whenthe bulk absorber layer 210 comprises TaSi or TaSiN; tantalum boronoxide based materials, such as TaBO, when the bulk absorber layer 210comprises TaBN; and oxidized and nitrogenized tantalum-based materials,such as TaON, when the bulk absorber layer 210 comprises TaN. Theantireflective coating layer 212 can also comprise TaO.

A patterned photoresist layer 214 is then formed over the absorber layer216 having openings 218 formed therein that expose portions 220 of theabsorber layer 216 for etching. The photoresist layer 214 may compriseany suitable photosensitive resist materials, such as an e-beam resist(for example, a chemically amplified resist (CAR)), and deposited andpatterned in any suitable manner. The photoresist layer may be depositedto a thickness between about 100 nm and about 1000 nm.

The photomask substrate 102 is readily to be transferred to an etchingprocessing chamber, such as the etch reactor 100 depicted withreferenced to FIG. 1, to perform an etching process. The embodimentdepicted in FIG. 2 shows a portion 224 of the absorber layer 216 hasbeen etched away and the endpoint detection system 164 is turned onduring the etching process to monitor the etching progress to determinea proper etching process endpoint, which will be discussed in detailfurther below with referenced to FIGS. 3-4B. The etching process isperformed to etch the absorber layer 216 and the capping layer 208exposed through the opening 218 defined by the photoresist layer 214.The etching process is performed to etch the absorber layer 216 and thecapping layer 208 until the underlying surface of the reflectivemulti-material layer 206 is exposed. The antireflective coating layer212 and the bulk absorber layer 210 may be continuously etched using oneprocess step, such as a single etchant chemistry, or separately etchedby multiple steps in one or different etching processes as needed. Thepatterns from the photoresist layer 214 are then transferred into theabsorber layer 216 through the etching process.

Subsequently, a reflective multi-material layer etching process isperformed to etch the reflective multi-material layer 206. Thereflective multi-material etching process uses an etching gas mixtureconfigured to etch the reflective multi-material layer 206 until adesired depth of the reflective multi-material layer 206 is removed, orthe underlying photomask substrate 102 is exposed. As the reflectivemulti-material layer 206 may include more than one types of thematerials, the etching gas mixture as selected is configured to havehigh etching capability to etch different materials as well asmaintaining high selectivity to the upper capping layer 208 and theabsorber layer 216 so as to maintain desired sidewall profiles tocomplete the photomask manufacture process.

FIG. 3 is a flow diagram of one embodiment of a method 300 for etchingan absorber layer formed in a film stack disposed on a photomask, suchas the absorber layer 216 formed in the film stack 200 depicted in FIG.2, and determining an etching process endpoint for etching the absorberlayer 216. Although the method 300 is described below with reference toa substrate utilized to fabricate a photomask, the method 300 may alsobe used to advantage in other photomask etching or any etchingapplications.

The method 300 begins at block 302 when the photomask substrate 102 istransferred to and placed on a substrate support member disposed in anetch reactor, such as the etching chamber depicted in FIG. 1. Asdescribed above, the photomask substrate 102 includes an opticallytransparent silicon based material, such as quartz or low thermalexpansion glass layer having the absorber layer 216 disposed thereonhaving portions 222 of absorber layer 216 exposed by the patternedphotoresist layer 214 readily for etching.

At block 304, an etching process is performed to etch the absorber layer216 disposed on the substrate 102. The patterned photoresist layer 214may serve as a mask layer to protect some portion of the absorber layer216 from being etched during the absorber layer etching process. Theetching process endpoint detection for etching the absorber layer 216can be monitored either in reflection or transmission mode, andreflectance, transmittance and/or interferometric signals can beperformed. In one particular embodiment depicted therein, the processendpoint detection for etching the absorber layer 216 is monitored inreflection mode.

In one embodiment, halogen-containing gases are typically used foretching different materials found on the film stack 200 of the photomaskstructure. For example, a process gas containing chlorine may be usedfor etching an absorber layer (e.g., a tantalum containing layer).Alternatively, a fluorine-containing gas such as trifluoromethane (CHF₃)or tetrafluoromethane (CF₄) may also be used for etching quartz. In oneembodiment, a fluorine-containing gas such as trifluoromethane (CHF₃) ortetrafluoromethane (CF₄) is often used to etch a TaO or TaBOantireflection layer while more selective chlorine and oxygen gascombinations are used to etch the TaN or TaBN absorber layer.

At block 306, while etching the absorber layer 216, an incident opticalbeam 750 from the endpoint detection system 164 is directed to theetched substrate surface. The incident optical beam 750, as shown inFIG. 2, from the etch rate detection system 164 is directed, through oneof the windows in the chamber lid, onto one or more areas of thephotomask substrate 102. The incident optical beam 750 is configured tobe directed to the opening 218, such as open areas where the absorberlayer 216 is exposed by the patterned photoresist layer 214 to be etchedto form trenches, vias, and apertures for the film stack 200 as needed.Alternatively, the plasma itself may be used as the light source.

A return beam 752, e.g., reflecting off the surface of etched absorberlayer 216 within the openings 218 being etched and exposed, is detectedby the photodetector 170 of the etch rate detection system 164.Alternatively, the return beam may be plasma light reflected off thephotomask at the directed areas. During etching of the absorber layer216, the intensity of the reflected optical beam 752 changes overtime.The time-varying intensity of the reflected optical beam 752 at aparticular wavelength is then analyzed to determine at least one of thedepth etched, the etch rate and the end point of the absorber layeretching process.

At block 308, an etching process endpoint is determined by analyzing thewaveform obtained from the detected reflected optical beam 752 reflectedfrom the surface of the etched substrate. In the embodiment wherein theabsorber layer 206 is a composite layer having the antireflectivecoating layer 212 disposed on the bulk absorber layer 210, the reflectedoptical beam 752 initially detected is for etching the antireflectivecoating layer 212. After the antireflective coating layer 212 is etchedaway, the reflected optical beam 752 may be continued to be collectedfor determination of the endpoint of etching the bulk absorber layer210. The endpoint detection process may be split into a two step processusing two different wavelengths, or the endpoint detection process maybe continuously performed using the same wavelength for detection untilthe whole bulk absorber layer 210 is etched away, exposing theunderlying capping layer 208. FIG. 4A depicts one embodiment of opticalsignals as detected for etch rate determination for etching theantireflective coating layer 212 at a light wavelength at between about200 nm and about 230 nm from the light source 166. The optical signal402, as shown in FIG. 4A, is plotted as a function of time to provide awaveform pattern corresponding to the varying intensity of the reflectedoptical beam 752 over time. The waveform pattern will be different atother wavelengths. Collecting a spectrum of wavelengths will providenumerous waveform patterns. The optical signal 402 is detected real-timewhen a production substrate is etched in the etch reactor. In theembodiment depicted in FIG. 4A, the intensity of the reflected opticalbeam 752 is gradually increasing as the underlying bulk absorber layer210 is gradually exposing. When the antireflective coating layer 212 isgradually etched away, the intensity of the reflected optical beam 752is gradually increasing until getting saturated. When the intensity ofthe reflected optical beam 752 is saturated and steady at a stable value404 at a time point 406, it indicates the antireflective coating layer212 has been etched away, exposing the underlying bulk absorber layer210, thereby determining the time point 406 is the proper endpoint foretching away the antireflective coating layer 212.

In one embodiment, an endpoint for etching the antireflective coatinglayer 212 may be determined when the intensity of the reflected opticalbeam 752 as detected is between about 1 percent and about 20 percent,such as between about 4 percent to 12 percent, for example about 5percent or 10 percent, increased from the initial detected reflectedoptical beam 752 collected in a beginning time point 403 of thedetection process. In another embodiment, the endpoint for etching theantireflective coating layer 212 may be determined when the slope of theoptical signal 402 is initially small, then rising by at least twotimes, then becoming small. In other word, the endpoint for etching theantireflective coating layer 212 is changed about 100 percent from theoriginal detected slope. In yet another embodiment, the endpoint foretching the antireflective coating layer 212 may be determined when theoptical signal 402 has become saturated and remains in a steady statefor about over than 3 seconds. In an exemplary embodiment wherein alight source of about 230 nm wavelength is utilized to detect theendpoint for etching the antireflective coating layer 212, the processendpoint occurred at time point 406 is between about 10 seconds andabout 25 seconds.

FIG. 4B depicts one embodiment of the optical signal 752 as detected foretch rate determination for etching the bulk absorber layer 210 at alight wavelength at between about 200 nm and about 800 nm, such asbetween about 200 nm and about 240 nm, from the light source 166 or theplasma source. The optical signal 410, as shown in FIG. 4B, is plottedas a function of time to provide a waveform pattern corresponding to thevarying intensity of the reflected optical beam 752 over time whenetching the bulk absorber layer 210. In the embodiment depicted in FIG.4B, the intensity of the reflected optical beam 752 is initially low andsomewhat decreasing, and then gradually increases as the bulk absorberlayer 210 is gradually etched away. When the bulk absorber layer 210 isgradually etched away exposing the underlying capping layer 208, theintensity of the reflected optical beam 752 is gradually increasinguntil getting saturated and becoming constant. When the intensity of thereflected optical beam 752 is saturated and steady at a stable value 414at a time point 412, it indicates the bulk absorber layer 210 has beensubstantially etched away, exposing the underlying capping layer 208,thereby determining the time point 412 is the proper endpoint foretching away the antireflective coating layer 212. As the bulk absorberlayer 210 is gradually etched away to expose the underlying cappinglayer 208, since the underlying capping layer 208 has a reflectivesurface, the reflectivity as detected raises when the underlying cappinglayer 208 is gradually exposing. The endpoint is then reached when thereflectivity raises and becomes constant.

In one embodiment, an endpoint for etching the bulk absorber layer 210may be determined when the intensity of the reflected optical beam 752as detected is about 5 percent or greater increased from the initialdetected reflected optical beam 752 collected from a beginning timepoint 408 of the detection process. In another embodiment, the endpointfor etching the bulk absorber layer 210 may be determined when the slopeof the optical signal 410 is about 0.01 per 10 seconds, changing fromabout 0.23 to about 0.24 (plasma source). In other word, the endpointfor etching the antireflective coating layer 212 is changed about 5percent or greater from the original detected slope. In yet anotherembodiment, the endpoint for etching the bulk absorber layer 210 may bedetermined when the optical signal 410 has become saturated and remainsin a steady state (or no longer increasing) for about more than 10seconds. In an exemplary embodiment wherein a light source of about 220nm wavelength is utilized to detect the endpoint for etching bulkabsorber layer 210, the process endpoint occurred at time point 412 isbetween about 25 seconds and about 175 seconds.

By monitoring reflectivity of an optical beam reflected from an etchedabsorber layer (either an antireflective coating or a bulk absorberlayer), such as a Ta containing material, at a predetermined wavelength,proper process endpoints may be obtained by analyzing waveforms obtainedfrom the reflected optical beam reflected from an etched substratesurface. The embodiments of the present invention provide an improvedapparatus and method with enhanced process monitoring and controlcapabilities. These improvements also allow reliable etch rate/loss ofthickness and endpoint determination for absorber layer etchingapplications.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of determining an etching endpoint of atantalum containing layer disposed on a substrate during an etchingprocess, comprising: performing an etching process on a tantalum andoxygen containing layer disposed on a first surface of a substratethrough a patterned mask layer in a plasma etch chamber; directing afirst radiation source having a first wavelength from about 200 nm andabout 800 nm from the first surface of the substrate to an areauncovered by the patterned mask layer; collecting a first optical signalreflected from the area covered by the patterned mask layer to obtain afirst waveform from the reflected first optical signal; analyzing afirst waveform obtained the reflected first optical signal reflectedfrom the first surface of the substrate from a first time point to asecond time point; determining a first endpoint of the etching processwhen a slope of the waveform is changed about 5 percent or greater fromthe first time point to the second time point; continuing etching atantalum containing and oxygen free layer disposed between the tantalumand oxygen containing layer and substrate; directing a second radiationsource having a second wavelength from about 200 nm and about 800 nmfrom the first surface of the substrate to an area uncovered by thepatterned mask layer and the etched tantalum containing and oxygen freelayer; collecting a second optical signal reflected from the areacovered by the patterned mask layer and the etched tantalum and oxygencontaining layer to obtain a second waveform from the reflected secondoptical signal; analyzing a second waveform obtained the reflectedsecond optical signal reflected from the first surface of the substratefrom a third time point to a fourth time point; and determining a secondendpoint of the etching process when a slope of the waveform is changedabout 5 percent or greater from the third time point to the fourth timepoint.
 2. The method of claim 1, wherein the tantalum containing andoxygen free layer is TaSi, a TaBN, or a TaN layer.
 3. The method ofclaim 1, wherein the tantalum and oxygen containing layer is a TaSiON, aTaBO, or a TaON layer.
 4. The method of claim 1, wherein the firstwavelength is about 220 nm, and the second wavelength is about 230 nm.5. The method of claim 1, wherein a reflective multi-material layer isdisposed between the tantalum containing and oxygen free layer and thesubstrate.
 6. The method of claim 5, wherein the reflectivemulti-material layer include at least one molybdenum layer and a siliconlayer.
 7. A method of determining an etching endpoint of a tantalumcontaining layer disposed on a substrate during an etching process,comprising: performing an etching process on a tantalum and oxygencontaining layer disposed on a first surface of a substrate through apatterned mask layer in a plasma etch chamber; directing a firstradiation source having a first wavelength from about 220 nm from thefirst surface of the substrate to an area uncovered by the patternedmask layer; collecting a first optical signal reflected from the areacovered by the patterned mask layer to obtain a first waveform from thereflected first optical signal; analyzing a first waveform obtained thereflected first optical signal reflected from the first surface of thesubstrate; determining a first endpoint of the etching process when thereflected first optical signal becomes saturated; continuing etching atantalum containing and oxygen free layer disposed between the tantalumand oxygen containing layer and substrate; directing a second radiationsource having a second wavelength about 230 nm from the first surface ofthe substrate to an area uncovered by the patterned mask layer and theetched tantalum containing and oxygen free layer; collecting a secondoptical signal reflected from the area covered by the patterned masklayer and the etched tantalum and oxygen containing layer to obtain asecond waveform from the reflected second optical signal; analyzing asecond waveform obtained the reflected second optical signal reflectedfrom the first surface of the substrate; and determining a secondendpoint of the etching process when the reflected second optical signalbecomes saturated.